RefCounted types should not have public destructors, printing/ and ui/

printing/backend/print_backend.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PRINTING_BACKEND_PRINT_BACKEND_H_
 #define PRINTING_BACKEND_PRINT_BACKEND_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 35 matching lines @@
 // PrintBackend class will provide interface for different print backends
 // (Windows, CUPS) to implement. User will call CreateInstance() to
 // obtain available print backend.
 // Please note, that PrintBackend is not platform specific, but rather
 // print system specific. For example, CUPS is available on both Linux and Mac,
 // but not available on ChromeOS, etc. This design allows us to add more
 // functionality on some platforms, while reusing core (CUPS) functions.
 class PRINTING_EXPORT PrintBackend
     : public base::RefCountedThreadSafe<PrintBackend> {
  public:
-  virtual ~PrintBackend();
-
   // Enumerates the list of installed local and network printers.
   virtual bool EnumeratePrinters(PrinterList* printer_list) = 0;
 
   // Get the default printer name. Empty string if no default printer.
   virtual std::string GetDefaultPrinterName() = 0;
 
   // Gets the capabilities and defaults for a specific printer.
   virtual bool GetPrinterCapsAndDefaults(
       const std::string& printer_name,
       PrinterCapsAndDefaults* printer_info) = 0;
 
   // Gets the information about driver for a specific printer.
   virtual std::string GetPrinterDriverInfo(
       const std::string& printer_name) = 0;
 
   // Returns true if printer_name points to a valid printer.
   virtual bool IsValidPrinter(const std::string& printer_name) = 0;
 
   // Allocate a print backend. If |print_backend_settings| is NULL, default
   // settings will be used.
   // Return NULL if no print backend available.
   static scoped_refptr<PrintBackend> CreateInstance(
       const base::DictionaryValue* print_backend_settings);
+
+ protected:
+  friend class base::RefCountedThreadSafe<PrintBackend>;
+  virtual ~PrintBackend();
 };
 
 }  // namespace printing
 
 #endif  // PRINTING_BACKEND_PRINT_BACKEND_H_